Contents1 Basic concepts of surveying 1

Definition – Basic measurements – Control networks – Locating position – Locatingtopographic detail – Computer systems – DGM – CAD – GIS – Vector/raster – Topology –Laser scanner – Summary – Units of measurement – Significant figures – Rounding offnumbers – Errors in measurement – Indices of precision – Weight – Rejection of outliers –Combination of errors

2 Vertical control 43

Introduction – Levelling – Definitions – Curvature and refraction – Equipment – Instrumentadjustment – Principle of levelling – Sources of error – Closure tolerances – Errordistribution – Levelling applications – Reciprocal levelling – Precise levelling – Digitallevelling – Trigonometrical levelling – Stadia tacheometry

3 Distance 117

Tapes – Field work – Distance adjustment – Errors in taping – Accuracies –Electromagnetic distance measurement (EDM) – Measuring principles – Meteorologicalcorrections – Geometrical reductions – Errors and calibration – Other error sources –Instrument specifications – Developments in EDM – Optical distance measurement (ODM)

4 Angles 178

The theodolite – Instrumental errors – Instrument adjustment – Field procedure – Measuringangles – Sources of error

5 Position 208

Introduction – Reference ellipsoid – Coordinate systems – Local systems – Computation onthe ellipsoid – Datum transformations – Orthomorphic projection – Ordnance SurveyNational Grid – Practical applications – The Universal Transverse Mercator Projection(UTM) – Plane rectangular coordinates

6 Control surveys 252

Traversing – Triangulation – Trilateration – Triangulateration – Inertial surveying

7 Satellite positioning 307

Introduction – GPS segments – GPS receivers – Satellite orbits – Basic principle of positionfixing – Differencing data – GPS field procedures – Error sources – GPS survey planning –Transformation between reference systems – Datums – Other satellite systems –Applications

8 Curves 347

Circular curves – Setting out curves – Compound and reverse curves – Short and/or small-radius curves – Transition curves – Setting-out data – Cubic spiral and cubic parabola –Curve transitional throughout – The osculating circle – Vertical curves

9 Earthworks 420

Areas – Partition of land – Cross-sections – Dip and strike – Volumes – Mass-hauldiagrams

10 Setting out (dimensional control) 464

Protection and referencing – Basic setting-out procedures using coordinates – Technique forsetting out a direction – Use of grids – Setting out buildings – Controlling verticality – Controllinggrading excavation – Rotating lasers – Laser hazards – Route location – Underground surveying– Gyro-theodolite – Line and level – Responsibility on site – Responsibility of the setting-outengineer

Index 517

vi Contents

1

Basic concepts of surveying

The aim of this chapter is to introduce the reader to the basic concepts of surveying. It is thereforethe most important chapter and worthy of careful study and consideration.

1.1 DEFINITION

Surveying may be defined as the science of determining the position, in three dimensions, ofnatural and man-made features on or beneath the surface of the Earth. These features may then berepresented in analog form as a contoured map, plan or chart, or in digital form as a three-dimensional mathematical model stored in the computer. This latter format is referred to as a digital

ground model (DGM).In engineering surveying, either or both of the above formats may be utilized in the planning,

design and construction of works, both on the surface and underground. At a later stage, surveyingtechniques are used in the dimensional control or setting out of the designed constructional elementsand also in the monitoring of deformation movements.

In the first instance, surveying requires management and decision making in deciding the appropriatemethods and instrumentation required to satisfactorily complete the task to the specified accuracyand within the time limits available. This initial process can only be properly executed after verycareful and detailed reconnaissance of the area to be surveyed.

When the above logistics are complete, the field work – involving the capture and storage of fielddata – is carried out using instruments and techniques appropriate to the task in hand.

The next step in the operation is that of data processing. The majority, if not all, of the computationwill be carried out by computer, ranging in size from pocket calculator to mainframe. The methodsadopted will depend upon the size and precision of the survey and the manner of its recording;whether in a field book or a data logger. Data representation in analog or digital form may now becarried out by conventional cartographic plotting or through a totally automated system using acomputer-driven flat-bed plotter. In engineering, the plan or DGM is used for the planning anddesign of a construction project. This project may comprise a railroad, highway, dam, bridge, oreven a new town complex. No matter what the work is, or how complicated, it must be set out onthe ground in its correct place and to its correct dimensions, within the tolerances specified. To thisend, surveying procedures and instrumentation are used, of varying precision and complexity,depending on the project in hand.

Surveying is indispensable to the engineer in the planning, design and construction of a project,so all engineers should have a thorough understanding of the limits of accuracy possible in theconstruction and manufacturing processes. This knowledge, combined with an equal understandingof the limits and capabilities of surveying instrumentation and techniques, will enable the engineerto successfully complete his project in the most economical manner and shortest time possible.

Basic concepts of surveying 9

1.5.1 Field survey

In the previous section, the method of locating detail by offsets was illustrated. In engineeringsurveys the more likely method is by polar coordinates, i.e. direction relative to a pair of selectedcontrol points, plus the horizontal distance from one of the known points, as shown in Figure 1.8.

The directions would be measured by theodolite and the distance by EDM, to a detail pole heldvertically on the detail (Figure 1.12); hence the ideal instrument would be the electronic tacheometeror total station.

The accuracy required in the location of detail is a function of the scale of the plan. For instance,if the proposed scale is 1 in 1000, then 1 mm on the plan would represent 1000 mm on the ground.If the plotting accuracy was, say, 0.2 mm, then the equivalent field accuracy would be 200 mm anddistance need be measured to no greater accuracy than this. The equivalent angular accuracy for alength of sight at 200 m would be about 3′ 20′′. From this it can be seen that the accuracy requiredto fix the position of detail is much less than that required to establish the position of control points.It may be, depending on the scale of the plan and the type of detail to be located, that stadiatacheometry could be used for the process, in the event of there being no other alternative.

The accuracy of distance measurement in stadia tacheometer (D = 100 × S cos2 θ), as shown inChapter 2, is in the region of 1 in 300, equivalent to 300 mm in an observation distance of 100 m.Thus before this method can be considered, the scale of the plan must be analysed as above, theaverage observation distance should be considered and the type of detail, hard or soft, reconnoitred.Even if all these considerations are met, it must be remembered that the method is cumbersome anduneconomical unless a direct reading tacheometer is available.

1.5.2 Plotting the detail

The purpose of the plan usually defines the scale to which it is plotted. The most common scale forconstruction plans is 1 in 500, with variations above or below that, from 1 in 2500 to 1 in 250.

The most common material used is plastic film with such trade names as ‘Permatrace’. This is an

Fig. 1.11 Metal template and punch

10 Engineering Surveying

Fig. 1.12 ‘Detail pole’ locating topographic detail

extremely durable material, virtually indestructible with excellent dimensional stability. When theplot is complete, paper prints are easily obtained.

Although the topographic detail could be plotted using a protractor for the direction and a scalefor the distances, in a manner analogous to the field process, it is a trivial matter to produce ‘in-house’ software to carry out this task. Using the arrangement shown in Figure 1.13, the directionsand distances are input to the computer, changed to two-dimensional coordinates and plotted direct.A simple question asks the operator if he wishes the plotted point to be joined to the previous oneand in this way the plot is rapidly progressed. This elementary ‘in-house’ software simply plotspoints and lines and the reduced level of the points, where the vertical angle is included. However,there is now an abundance of computer plotting software available that will not only produce acontoured plot, but also supply three-dimensional views, digital ground models, earthwork volumes,road design, drainage design, digital mapping, etc.

1.5.3 Computer systems

To be economically viable, practically all major engineering/surveying organizations use an automatedplotting system. Very often the total station and data logger are purchased along with the computerhardware and software, as a total operating system. In this way interface and adaptation problemsare precluded. Figure 1.14 shows such an arrangement including a ‘mouse’ for use on the digitizingtablet. An AO flat-bed plotter is networked to the system and located separately.

The essential characteristics of such a system are:

(1) Capability to accept, store, transfer, process and manage field data that is input manually ordirectly from an interfaced data logger (Figure 1.15).

(2) Software and hardware to be in modular form for easy accessing.(3) Software to use all modern facilities, such as ‘windows’, different colour and interactive screen

graphics, to make the process user friendly.(4) Continuous data flow from field data to finished plan.

Basic concepts of surveying 11

Fig. 1.13 Computer driven plotter

Fig. 1.14 Computer system with digitizing tablet

(5) Appropriate data-base facility, for the storage and management of coordinate and cartographicdata necessary for the production of digital ground models and land/geographic informationsystems.

(6) Extensive computer storage facility.(7) High-speed precision flat-bed or drum plotter.

12 Engineering Surveying

To be truly economical, the field data, including appropriate coding of the various types of detail,should be captured and stored by single-key operation, on a data logger interfaced to a total station.The computer system should then permit automatic transfer of this data by direct interface betweenthe logger and the system. The modular software should then: store and administer the data; carryout the mathematical processing, such as network adjustment, production of coordinates and elevations;generate data storage banks; and finally plot the data on completion of the data verification process.

Prior to plotting, the data can be viewed on the screen for editing purposes. This can be done fromthe keyboard or by light pen on the screen using interactive graphics routines. The plotted detail canbe examined, moved, erased or changed, as desired. When the examination is complete, the commandto plot may then be activated. Figure 1.16 shows an example of a computer plot.

1.5.4 Digital ground model (DGM)

A DGM is a three-dimensional, mathematical representation of the landform and all its features,stored in a computer data base. Such a model is extremely useful in the design and constructionprocess, as it permits quick and accurate determination of the coordinates and elevation of anypoint.

The DGM is formed by sampling points over the land surface and using appropriate algorithmsto process these points to represent the surface being modelled. The methods in common use aremodelling by ‘strings’, ‘regular grids’ or ‘triangular facets’. Regardless of the methods used, theywill all reflect the quality of the field data.

A ‘string’ comprises a series of points along a feature and so such a system stores the position offeatures surveyed. It is widely used for mapping purposes due to its flexibility, its accuracy alongthe string and its ability to process large amounts of data very quickly. However, as it does not storethe relationship between strings, a searching process is essential when the levels of points not

Fig. 1.15 Data logger

GATE Study Material Surveying (CivilEngineering)

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